So when you exert your muscles to the point that aerobic metabolism can't keep up with the energy demands, it switches over to anaerobic and starts depleting the glycogen storage in your fast twitch muscle fibers (or maybe it was slow twitch... I really don't remember and don't feel like going though my notes). When that's gone your muscles have reached fatigue and you literally cannot move the muscles anymore. This generally only happens after keeping up high intensity aerobic exercise for long periods of time.

You don't run out of fuel when you hit the wall. You run out of glycogen and have to start burning fat which is harder for the body to burn. You can go past hitting the wall but it takes a little while.

Hitting the wall is when you're muscles run out of glycogen to fuel them and you have to start metabolising other stuff to keep running. Usually marathon runners and whatever will hit it at around 16 miles I've heard. So I'm guessing that this guy's muscles got full of lactic acid and just failed instead

unlike some of the fat bastards we get in the world, this guy gave it his all and still tried to go on. it shows pure willpower rather than athletic ability (something that only very few people actually have).

most of the crowd were probably more proud of him than they were of the winner